Planar Transformer Core Isolation for Shock and Vibration
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Solution Overview
Problem
Planar transformers in military and aeronautic applications are prone to high g-force shocks and vibrations, which can cause the core to move and risk electrical shorting of windings through the conductive core material.
Innovation Solution
A planar transformer design with a ferromagnetic core and electrically independent windings separated by dielectric substrates, using pre-form adhesive sheets to bond the core to a multilayer PWB, and anti-abrasion substrates to prevent shorting during high g-force shocks and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the core is allowed to move freely in the transformer assembly, then the manufacturing and assembly process is simpler, but the core may contact the windings during high g-force shocks and vibrations causing electrical shorts
Solution Approach 1:
A non-conductive adhesive is introduced as an intermediary substance between the ferromagnetic core and the PWB. This adhesive mediator prevents direct contact between the core and conductive elements while maintaining the core in its proper position, thus preventing electrical shorts without complicating the assembly process
Solution Approach 2:
The non-conductive adhesive is applied beforehand to the core or PWB surface before final assembly. This pre-applied adhesive creates a protective barrier that cushions against the harmful effects of high g-force shocks and vibrations, preventing the core from contacting the windings during extreme conditions
2Stability of the object's composition
If a rigid adhesive is used to bond the core to the PWB, then the core position is stable during shocks and vibrations, but the adhesive may not fill gaps effectively between components
Solution Approach 1:
The adhesive's physical parameters (viscosity, flow characteristics) are changed by controlling its formulation and curing properties. The adhesive is designed to be sufficiently fluid during application to fill gaps and conform to surfaces, then cures to provide the required rigid bonding and positional stability during high g-force conditions
Solution Approach 2:
A composite adhesive system is used that combines multiple materials or phases - typically a resin matrix with reinforcing fillers. This composite structure provides both the gap-filling capability of a fluid material and the rigid, stable bonding required to prevent core movement during shocks and vibrations
3Force
If the adhesive is made highly rigid after curing, then it effectively prevents core movement during high g-force shocks, but it may create stress concentrations that could lead to cracking
Solution Approach 1:
The adhesive system exhibits local quality variations - being more compliant or flexible in regions where stress concentrations might occur, and more rigid in regions where positional stability is critical. This localized property variation allows the adhesive to resist shock forces while distributing stresses to prevent cracking
Solution Approach 2:
The adhesive's mechanical parameters are optimized through material formulation and curing control to achieve a balance between rigidity and toughness. The cured adhesive maintains sufficient rigidity to prevent core movement during high g-force shocks while incorporating features that distribute stress and prevent crack propagation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively prevents electrical shorting of windings by maintaining core separation from windings, ensuring reliable operation under extreme conditions.
Implementation Method 1
When heated, the first and second pre-form adhesive sheets become viscous to respectively effectuate a bonding between the first and second parts of the core and the top and bottom surfaces of the PWB
Implementation Method 2
The PWB includes electrically independent primary and secondary windings surrounding the aperture that are magnetically coupled by the core
Data Source
AI summary
A planar transformer including first and second parts of a core with least one of the first and second parts having a center post that resides in an aperture of a PWB. The PWB includes primary windings and secondary windings that surround the center post, are magnetically coupled by the core, and are electrically independent. Separating an uppermost winding from the first part of the core is a first prepreg structure and separating a lowermost winding from the second part of the core is a second prepreg structure. There being no windings disposed between the first and second prepreg structures and the core. This planar transformer structure inhibits the windings from electrically shorting through the core when the planar transformer is subjected to shock or vibration. One variant includes the use of pre-form adhesives sheets located between the solder mask layers of the PWB and the core that further inhibit the windings from shorting through the core.